Traditional positive displacement (reciprocating piston) compressor assemblies include a compressor coupled to a motor using belt drive or direct drive mechanisms which transfer power from the motor to the compressor for reciprocating the piston (or pistons) of the compressor. Conventionally, in such belt drive and direct drive configurations, the drive shaft of the motor (herein after referred to as the motor shaft) and the crank shaft of the compressor (hereinafter referred to as the compressor shaft) turn in the same direction to simplify the drive train of the compressor assembly.
A significant problem with reciprocating piston compressors is that the torque of the compressor shaft varies significantly during rotation of the shaft (i.e., reciprocation of the piston) causing excessive torsional vibration of the compressor assembly. In the past, three common methods have been used for reducing such torsional vibration. The first of these methods was to divide the compressor displacement into several smaller piston/cylinder assemblies. The second method was to increase the size and moment of inertia of the compressor flywheel. These solutions add cost and size to the compressor and have practical upper limits. The third method involved increasing compressor speed. However, this solution also generates excessive noise and increases reciprocating imbalance. Moreover, the effectiveness of all three solutions is limited to reduction rather than elimination of torsional vibration and requires compromise between the types of imbalance and noise reduction.
Consequently, it is desirable to provide a compressor assembly having a reciprocating piston compressor driven by a motor, wherein torsional vibration in the compressor assembly is greatly reduced or eliminated.